I can only get Apple's Mail program to talk to KC using the 'password' method. This is called 'Login' in KC, I think.

If I turn off 'plain' and 'login' as acceptable login methods in KC, then I can't find an authentication method in Apple Mail which will talk to KC. Unfortunately the PCI-DSS compliance police now require us not to use Login or Plain on any internet-facing ports.

as an update, it seems that I only have difficulties with SMTP log in. Exchange IMAP works fine with MD5 Challenge-Response, but if I choose that option for SMTP then it keeps asking for my password (which it doesn't accept).

I've seen intermittent issues with smtp and md5 in apple's mail.app on mac os 10.6.x. I usually have the user switch to plain, temporarily to get messages sent. Then switch it back after reboot. It rarely happens, and our users connect over ssl, so it's never been a pressing concern. I'd speculate its a bug with mail.app, as restarting smtp services in connect have zero effect. Also seems to correlate with sketchy network connections, like when users are connecting from their mediocre home ISP. Maybe it's a latency issue? Maybe mail.app holds onto a bad cache too long? Either way, it's far from universal.

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